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The present invention relates generally to testing vehicles and more specifically to test vehicles for evaluating resistance characteristics of materials arranged into test samples.
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Many different materials are considered for semiconductor and related applications because of their resistive and other properties. These materials need to be analyzed to precisely determine their properties and applicability. Often this analysis involves forming test samples from the evaluated materials. The test samples often need to have shapes and/or sizes comparable to actual components of integrated circuits that these materials are considered for. Furthermore, the test samples often need to be tested at conditions (e.g., applied voltages, provided interface materials) that are comparable to ones used in the integrated circuits. Finally, compositional, geometrical, and other variations may result in a great number of possible test samples. For example, resistive random access memory (ReRAM) cells may include multiple layers, such as resistive switching layer, electrodes, embedded resistors, coupling layers, and the like. Each of these layers may be made from a variety of different materials. Performance of individual layers (e.g., varying compositions and thicknesses of each layer) and various combinations of these layers (e.g., varying materials in two adjacent layers) need to be tested. All these present unique challenges for test vehicles.
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Provided are test vehicles for evaluating various semiconductor materials. These materials may be used for various integrated circuit components, such as embedded resistors of resistive random access memory cells. Also provided are methods of fabricating and operating these test vehicles. A test vehicle may include two stacks protruding through an insulating body. Bottom ends of these stacks may include n-doped poly-silicon and may be interconnected by a connector. Each stack may include a titanium nitride layer provided over the poly-silicon end, followed by a titanium layer over the titanium nitride layer and a noble metal layer over the titanium layer. The noble metal layer extends to the top surface of the insulating body and forms a contact surface. The titanium layer may be formed in-situ with the noble metal layer to minimize oxidation of the titanium layer, which is used as an adhesion layer and oxygen getter.
In some embodiments, a test vehicle for evaluating resistance characteristics of test materials formed into test samples includes a connector, a body, and two stacks, each protruding through the body and making an electrical connection to the connector. The connector electrically interconnects the two stacks and includes a conductive material, such as tungsten. The connector may have a predetermined resistance between the stacks, such as between about 5 kOhm and 120 kOhm, such as 9 kOhm, about 62 kOhm, and about 116 kOhm. When multiple test vehicles are provided on the same substrate, some vehicles may have connectors with different resistances. In some embodiments, the two stacks of the same test vehicle are positioned between 1 micrometer and 100 micrometers from each other.
The body includes an insulating material, such as silicon dioxide. Each of the two stacks includes a layer made of titanium and another layer made of a noble metal, such as platinum, iridium, or ruthenium. The thickness of the titanium layer may be between about 20 Angstroms to 70 Angstroms, for example, about 50 Angstroms. The thickness of the noble metal layer may be between about 20 Angstroms to 70 Angstroms, for example, about 50 Angstroms. The noble metal layer extends to the top surface of the body and provides a contact surface.
In some embodiments, each of the two stacks includes another layer provided between the titanium layer and the connector. This other layer may be made from n-doped polysilicon. Furthermore, each stack may also include a titanium nitride layer provided between the titanium layer and the n-doped polysilicon layer.
In some embodiments, each stack has a height of between about 200 nanometers and 1,000 nanometers. Generally, this height corresponds to the thickness of the body. In some embodiments, the contact surface of at least one stack has a dimension of between about 100 nanometers and 600 nanometers within the plane of the substrate (i.e., substantially perpendicular to the height of the stack). This dimension may represent a length of a side of a square or a diameter of a circle. The two stacks of the same test vehicle may have differently sized contact surfaces. Furthermore, a substrate may have multiple test vehicles with differently sized contact surfaces.
In some embodiments, the test vehicle includes two contact pads provided over each of the contact surfaces. A first contact pad may directly interface with a first of the contact surfaces, while a second contact pad may be positioned over a test sample formed from a test material. The test sample is provided between this second contact pad and the second contact surface. The test sample may have dimensions comparable to a corresponding IC component (e.g., the thickness of a test sample may be comparable to the thickness of an embedded resistor). The test sample may extend beyond the boundaries of the corresponding contact surface, which means that the area of this contact surface determines the interface between these two components. Dimensions of the contact pads may be between about 1 micrometer and 100 micrometers within the plane substantially perpendicular to the height of the stack. These dimensions are sufficient to make external electrical connections to the contact pads, such as with probes during actual resistance measurements.
Provided also is a die including a substrate, a first test vehicle, and a second test vehicle. Each test vehicle includes two stacks, each stack having a first layer and a second layer. The first layer may be made from a noble metal, while the second layer may be made from titanium. The first layers of each stack provide corresponding contact surfaces. The two stacks of the first test vehicle are interconnected with a first connector. The two stacks of the second test vehicle are interconnected with a second connector. The first connector may have a different resistance than the second connector. In some embodiments, at least one contact surface of the first test vehicle has a different area a contact surface of the second test vehicle.
Provided also is a method of forming a test vehicle for evaluating resistance characteristics of materials. The method may involve providing a substrate into a processing chamber and forming a titanium layer on the substrate. Without breaking vacuum in the processing chamber, another layer including a noble metal is formed over the titanium layer, such that the noble metal layer caps the titanium layer. The method may proceed with etching portions of the two layers thereby forming two stacks. The two stacks are electrically connected by a connector provided in the substrate. The method then proceeds with filling the space between the two stacks with an insulating material. The top surfaces of the two stacks are exposed and form contact surfaces of the test vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
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To facilitate understanding, the same reference numerals have been used, where possible, to designate common components presented in the figures. The drawings are not to scale and the relative dimensions of various elements in the drawings are depicted schematically and not necessarily to scale. Various embodiments can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
FIG. 1A illustrates a schematic diagram of combinatorial processing and evaluation using primary, secondary, and tertiary screening, in accordance with some embodiments.
FIG. 1B illustrates a schematic diagram representing a general methodology for combinatorial process sequence integration involving site isolated processing and/or conventional processing, in accordance with some embodiments.
FIG. 2A illustrates a schematic representation of a substrate having eight site isolation regions, in accordance with some embodiments.
FIG. 2B illustrates a schematic representation of a site isolation regions having twelve dies, in accordance with some embodiments.
FIG. 2C illustrates a schematic representation of a dies having three test chips, each test chip including four test sites, in accordance with some embodiments.
FIG. 2D illustrates a schematic top view a test site illustrating various components of a test vehicle provided on the test site, in accordance with some embodiments.
FIG. 2E illustrates a schematic cross-sectional representation of a test vehicle, in accordance with some embodiments.
FIG. 3 illustrates a process flowchart corresponding to a method of fabricating a test vehicle, in accordance with some embodiments.
FIG. 4A-4C illustrates a schematic representation of a test vehicle during various stages of its fabrication, in accordance with some embodiments.
FIG. 5 illustrates a process flowchart corresponding to a method of testing the resistance of a sample using a test vehicle, in accordance with some embodiments.
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A detailed description of various embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.
Screening semiconductor materials often require special test vehicles that allow imitating certain characters of integrated circuits and generating representative test results. For example, test samples made from tested materials may need to be comparable in size and/or shape to specific components of the integrated circuit, need to interface with specific materials, and need to be processed in a particular manner prior to and during testing.
One characteristic of a material that is important for many semiconductor applications is its electrical resistivity. Resistivity, which is also known as specific electrical resistance, is a measure of how strongly the material opposes the flow of an electric current through the material. Resistivity may be influenced by material composition, applied voltages (e.g., experience a breakdown), and other factors. Measuring resistivities of various materials, particularly nanoscale structures, may be important and difficult at the same time.
One specific example of a semiconductor device that is particularly sensitive to resistive characteristics of its components is a ReRAM cell. For example, embedding a resistor in series with other components of a ReRAM cell, such as a resistive switching layer, limits the current through the cell. This embedded resistor feature is used for controlling operations of the ReRAM cell and protecting it from being damaged.
For example, an embedded resistor formed into a square block of about 10-20 nanometers per side and a thickness of about 100 Angstroms may need to have a resistance of 100-200 kOhm. Furthermore, an embedded resistor should have a constant resistance over the entire operating voltage range of the ReRAM cell (e.g., up to 10 V). It has been found that some materials experience a break down such that their resistivities change in an abrupt manner upon reaching certain voltages.